L-asparaginases from Mycobacterium tuberculosis strains H37Rv and H37Ra

Marine microbial L-asparaginase: Biochemistry, molecular approaches and applications in tumor therapy and in food industry

The marine environment is a rich source of biological and chemical diversity. It covers more than 70% of the Earth's surface and features a wide diversity of habitats, often displaying extreme conditions, where marine organisms thrive, offering a vast pool for microorganisms and enzymes. Given the dissimilarity between marine and terrestrial habitats, enzymes and microorganisms, either novel or with different and appealing features as compared to terrestrial counterparts, may be identified and isolated. L-asparaginase (E.C. 3.5.1.1), is among the relevant enzymes that can be obtained from marine sources. This amidohydrolase acts on L-asparagine and produce L-aspartate and ammonia, accordingly it has an acknowledged chemotherapeutic application, namely in acute lymphoblastic leukemia. Moreover, L-asparaginase is also of interest in the food industry as it prevents acrylamide formation. Terrestrial organisms have been largely tapped for L-asparaginases, but most failed to comply with criteria for practical applications, whereas marine sources have only been marginally screened. This work provides an overview on the relevant features of this enzyme and the framework for its application, with a clear emphasis on the use of L-asparaginase from marine sources. The review envisages to highlight the unique properties of marine L-asparaginases that could make them good candidates for medical applications and industries, especially in food safety.

The role of glutamine oxoglutarate aminotransferase and glutamate dehydrogenase in nitrogen metabolism in Mycobacterium bovis BCG

Recent evidence suggests that the regulation of intracellular glutamate levels could play an important role in the ability of pathogenic slow-growing mycobacteria to grow in vivo. However, little is known about the in vitro requirement for the enzymes which catalyse glutamate production and degradation in the slow-growing mycobacteria, namely; glutamine oxoglutarate aminotransferase (GOGAT) and glutamate dehydrogenase (GDH), respectively. We report that allelic replacement of the Mycobacterium bovis BCG gltBD-operon encoding for the large (gltB) and small (gltD) subunits of GOGAT with a hygromycin resistance cassette resulted in glutamate auxotrophy and that deletion of the GDH encoding-gene (gdh) led to a marked growth deficiency in the presence of L-glutamate as a sole nitrogen source as well as reduction in growth when cultured in an excess of L-asparagine.

DevR-mediated adaptive response in Mycobacterium tuberculosis H37Ra: links to asparagine metabolism

The DevR transcriptional switch that defines the response of Mycobacterium tuberculosis to the lack of oxygen is now well established and likely helps the bacteria shift to a state of persistence. The M. tuberculosis two component signal transduction system (TCS), DevR-DevS, implicated in this transition to latency, is differentially expressed in H37Ra and H37Rv strains. Despite originating from the H37 ancestral strain, H37Ra and H37Rv have significant differences in their growth, physiology, and virulence. To further dissect the role of DevR in growth adaptive processes of M. tuberculosis, we investigated the hypoxic response of the avirulent H37Ra strain. Our results show that the DevR-DevS TCS in H37Ra is responsive to hypoxia and capable of target gene regulation, indicating similar DevR-DevS signaling pathways in H37Ra and H37Rv. A key finding of this study was the constitutive expression of the Rv3134c-devR-devS operon and a subset of sentinel DevR-regulated genes in aerobic cultures of H37Ra but not H37Rv grown in Dubos-Tween-albumin medium. Asparagine and/or catabolites of asparagine metabolism were implicated in aerobic induction of the DevR-DevS TCS in H37Ra. This is the first report of medium-specific constitutive expression of the DevR regulon in an avirulent strain and suggests a potential role for metabolite(s) in the activation of the DevR-DevS TCS.

Extracellular enzyme activities potentially involved in the pathogenicity of Mycobacterium tuberculosis

To evaluate the potential contribution of extracellular enzymes to the pathogenicity of mycobacteria, the presence of selected enzyme activities was investigated in the culture filtrates of the obligate human pathogen Mycobacterium tuberculosis, M. bovis BCG, the opportunistic pathogens M. kansasii and M. fortuitum, and the non-pathogenic species M. phlei and M. smegmatis. For M. tuberculosis and M. bovis, 22 enzyme activities were detected in the culture filtrates and/or cell surfaces, of which eight were absent from the culture fluids of non-pathogens: alanine dehydrogenase, glutamine synthetase, nicotinamidase, isonicotinamidase, superoxide dismutase, catalase, peroxidase and alcohol dehydrogenase. These activities, which correspond to secreted enzymes, formed a significant part (up to 92%) of the total enzyme activities of the bacteria and were absent from the culture fluids and the cell surfaces of the non-pathogenic species M. smegmatis and M. phlei. The extracellular location of superoxide dismutase and glutamine synthetase seemed to be restricted to the obligate pathogens examined. The difference in the enzyme profiles was not attributable to the growth rates of the two groups of bacteria. The presence of the eight enzyme activities in the outermost compartments of obligate pathogens and their absence in those of non-pathogens provides further evidence that these enzymes may be involved in the pathogenicity of mycobacteria. In addition, the eight enzyme activities were demonstrated in the cell extract of M. smegmatis. Stepwise erosion of the cell surface of M. smegmatis to expose internal capsular constituents showed that the various enzyme activities, with the possible exception of superoxide dismutase, were located more deeply in the cell envelope of this bacterium. This suggests that the molecular architecture of the mycobacterial envelopes may play an important role in the pathogenicity of these organisms.

A specific L-asparaginase from Thermus aquaticus

The L-asparaginase from an extreme thermophile, Thermus aquaticus strain T351, was highly substrate- and stereospecific, with no activity against glutamine or D-asparagine. It had a high Km of 8.6 mM. In these aspects it closely resembled the corresponding enzymes from thermophilic bacteria. The enzyme had a molecular weight of 80,000, an isoelectric point of 4.6, and a pH optimum of 9.5. It showed some substrate inhibition above 20 mM asparagine and was also inhibited by L-aspartic acid, D- and L-lysine (Ki of 5.2 and 1.25 mM, respectively), and D- and L-serine. The half-life of the enzyme at 85 degrees C was 40 min. The Arrhenius plot showed a change in slope at 55 degrees C.

The purification and some properties of a stereospecific D-asparaginase from an extremely thermophilic bacterium, Thermus aquaticus

A specific D-asparaginase was isolated and crystallized from Thermus aquaticus strain T351. It is present in larger amounts than the L-asparaginase. The enzyme has a molecular weight of 60 000, an isoelectric point of 4.8 and a Km of 2 mM. It has 6 disulphide bonds/molecule, and a histidine residue at the active site. It is inhibited by keto acids and by high salt concentrations.

Tumor inhibitory and non-tumor inhibitory L-asparaginases from Pseudomonas geniculata

Two enzymes that catalyze the hydrolysis of l-asparagine have been isolated from extracts of Pseudomonas geniculata. After initial salt fractionation, the enzymes were separated by chromatography on diethylaminoethyl-Sephadex and purified to homogeneity by gel filtration, ion-exchange chromatography, and preparative polyacrylamide electrophoresis. The enzymes differ markedly in physicochemical properties. One enzyme, termed asparaginase A, has a molecular weight of approximately 96,000 whereas the other, termed asparaginase AG, has a molecular weight of approximately 135,000. Both enzymes are tetrameric. The asparaginase A shows activity only with l-asparagine as substrate, whereas the asparaginase AG hydrolyzes l-asparagine and l-glutamine at approximately equal rates and it is also active with d-asparagine and d-glutamine as substrates. The asparaginase A was found to be devoid of antitumor activity in mice, whereas the asparaginase AG was effective in increasing the mean survival times of both C3H mice carrying the asparagine-requiring Gardner 6C3HED tumor line and Swiss mice bearing the glutamine-requiring Ehrlich ascites tumor line. These differences in antitumor activity were related to differences in the K(m) values for l-asparagine for the two enzymes. The asparaginase A has a K(m) value of 1 x 10(-3) M for this substrate whereas the corresponding value for the AG enzyme is 1.5 x 10(-5) M. Thus the concentration of asparagine necessary for maximal activity of the asparaginase A is very high compared with that of the normal plasma level of asparagine, which is approximately 50 muM.

Activity of L-asparaginase in cells of Streptomyces karnatakensis

Eight isolates capable of producing varying quantities of L-asparaginase and all identified as members of the genus Streptomyces were isolated from the soil and a suitable technique for the assay of intracellular L-asparaginase in actinomycetes was developed. The most potent L-asparaginase producer was identified as a strain of Streptomyces karnatakensis. Static cultures of S. karnatakensis showed maximum enzyme activity with almost maximum growth while shaken cultures exhibited their activity after 48 hours of growth. This phenomenon is discussed in terms of possible feedback mechanism and/or the biosynthesis of certain pigments. L-asparaginase of S. karnatakensis proved to be mostly intracellular and the presence of L-asparagine in the culture medium though, stimulating yet not essential for the enyzme biosynthesis. Cells grown on L-asparagine showed amidase activity with other amides but at a reduced rate.

Studies on the purification and characterization of malate dehydrogenase from Mycobacterium phlei

Malate dehydrogenase (L-malate:NAD+ oxidoreductase, EC 1.1.1.37) was purified from Mycobacterium phlei using (NH4)2SO4 precipitation followed by chromatography on Sephadex G-200, DEAE-cellulose on DEAE Sephadex A-50. The purified preparation homogeneous on column chromatography, polyacrylamide gel electrophoresis and sodium dodecyl sulphate gel electrophoresis had a molecular weight of 86 860. The native enzyme was composed of four subunits of equal molecular weight (21 550) and was thermostable upto 50 degrees C for 15 min. Some kinetic constants of the enzyme was determined. Tyrosine and isoleucine were identified as the N- and C-terminal amino acids respectively. The effects of various activators and inhibitors on the activity of the purified enzyme were studied. The purified enzyme exhibited maximum excitation and emission at 278 and 345 nm respectively. Amino acid composition of the enzyme was determined. Treatment of the enzyme with acid and urea resulted in dissociation of the enzyme followed by loss of catalytic activity. The dissociated enzyme could however be reconstituted by bringing the pH back to neutrality or by removal of urea from the enzyme solution.

Purification and Some Biological Properties of Asparaginase from Azotobacter vinelandii

Asparaginase was found in the soluble fraction of cells of Azotobacter vinelandii , and its activity remained the same during growth of the organism in a nitrogen-free medium. The specific activity and the yield of A. vinelandii increased twofold in the presence of ammonium sulfate. Within limits, the temperature (30 to 37°C) and pH (6.5 to 8.0) of the medium showed little effect on the levels of enzyme activity. The enzyme was purified to near homogeneity by standard methods of enzyme purification, including affinity chromatography, and had optimum activity at pH 8.6 and 48°C. The approximate molecular weight was 84,000. The apparent K m value for the substrate was 1.1 × 10 -4 M. Metal ions or sulfhydryl reagents were not required for enzyme activity. Cu 2+ , Zn 2+ , and Hg 2+ showed concentration-dependent inhibition, whereas amino and keto acids had no effect on the enzyme activity. Asparaginase was stable when incubated with rat serum and ascites fluid. The enzyme had no effect on the membrane of sheep erythrocytes and did not inhibit the incorporation of radioactive precursors into deoxyribonucleic acid, ribonucleic acid, and protein in Yoshida ascites sarcoma cells. Asparaginase activity was not detected in the tumor cells.

Factors influencing L-asparaginase production by staphylococci

Cultural and nutritional requirements for a maximum synthesis of 1-asparaginase by staphylococci were determined. The best production of the enzyme was found in the stationary phase of growth of a batch culture. The highest 1-asparaginase yield was obtained when the culture were aerated during an exponential phase of growth and further incubated in the stationary phase. Optimum pH for the enzyme production was 7.5. Glucose inhibited the enzyme formation. Maximum yield of 1-asparaginase was obtained when casein hydrolysate and yeast extract were supplied as carbon and nitrogen sources. Repression by 1-asparagine and 1-aspartic acid was absent.

Effect of L-asparagine on growth of Mycobacterium tuberculosis and on utilization of other amino acids

l-Asparagine controls the utilization of other amino acids by Mycobacterium tuberculosis (H37Ra) in aerated, liquid synthetic media. In a mixture containing asparagine and either l-alanine or l-glutamic acid, amino acid utilization is diphasic, with asparagine being utilized first. Short-term growth rates and cell yields are diminished and mimic those seen with asparagine alone. Catabolite repression is the probable regulatory mechanism responsible for this effect of asparagine. In contrast, in the presence of aspartic acid, asparagine stimulates growth and increases utilization of aspartic acid.

L-Asparaginase from Proteus vulgaris

To produce an immunologically and enzymologically new type of l-asparaginase, 108 strains of bacteria were screened for enzyme production. As a result, 13 bacteria belonging to the genera Alcaligenes, Bacterium, and Proteus were found to produce l-asparaginases in high levels. Among these l-asparaginases, partially purified l-asparaginases from B. cadaveris and P. vulgaris showed antitumor activity. A partially purified l-asparaginase preparation of P. vulgaris did not react with the antibody of Escherichia colil-asparaginase on the Ouchterlony agar plate. Culture conditions for the production of l-asparaginase by P. vulgaris were investigated in detail. The enzyme was produced in high yields when cells were grown aerobically in a medium containing sodium fumarate and corn steep liquor. The addition of glucose or ammonium ion to the medium, however, resulted in depressed production of l-asparaginase. Under the optimum conditions, 3,700 international units of l-asparaginase was obtained from 1 liter of culture medium.

Purification and properties of L-asparaginase from Serratia marcescens

The purification and properties of a tumor inhibitory l-asparaginase from Serratia marcescens are described. The following properties of the enzyme were examined: kinetics of the enzyme reaction, catalytic activity as a function of pH, boundary sedimentation velocity, electrophoresis on polyacrylamide gel, immuno-electrophoresis against homologous and heterologous antisera, immunodiffusion, blood clearance rate in mice, and inhibition of the 6C3HED lymphoma in C3H mice. Complete regression of this tumor was obtained with a smaller dose of the enzyme from S. marcescens than with enzyme from Escherichia coli. The reason for this difference was not evident from a comparison of several properties of the two enzymes.

Utilization of Amino Acids During Growth of Mycobacterium tuberculosis in Rotary Cultures

Marked differences were observed in the response of actively growing cells of the saprophyte, Mycobacterium smegmatis 607, and the avirulent human strain, M. tuberculosis (H37Ra), to several different nitrogen sources in aerated (rotary) cultures. The growth-promoting effect and utilization of equimolar concentrations (5 μmoles/ml) of l -alanine, l -aspartic acid, monosodium glutamate, or ammonium chloride were compared with that of l -asparagine, the normal nitrogen source, in Sauton synthetic liquid medium. The saprophyte grew equally well with each nitrogen source. However, marked differences were seen with H37Ra. Based on the rate of growth and cell yield, the relative growth-promoting effect of the amino acids for H37Ra is: alanine ≫ glutamate > asparagine > aspartic. Utilization of alanine, glutamate, and aspartic correlated well with growth. In contrast, utilization of asparagine during early growth of H37Ra was severalfold greater than that of either alanine or glutamate. Extracellular amino acids accumulated during the metabolism of asparagine but not during the utilization of the other nitrogen sources. Balanced metabolism of asparagine does not take place during aerated growth of H37Ra in asparagine media. During the metabolism of l -asparagine by M. tuberculosis (H37Ra) in aerated liquid cultures, metabolic controls may be exerted which impede protein synthesis.

Conditions for the production of L-asparaginase 2 by coliform bacteria

Of 28 coliforms, five strains of Escherichia coli were particularly active in elaborating L-asparaginase 2, the form of the enzyme useful in the treatment of some forms of cancer. Since it is advantageous to start purification of the enzyme from highly active cells, cultural conditions necessary for good growth and high enzyme yield have been studied. Gentle aeration proved suitable for good growth as well as high enzyme content. Stationary cultures gave poor growth, whereas vigorous aeration gave good growth but resulted in a marked decrease in the enzyme content of the cells. L-Asparaginase 2 has been purified about 40-fold by a combination of ammonium sulfate and ethyl alcohol precipitations.